#include <iostream>
#include <cmath>
using namespace std;

const double TINY_VALUE = 1e-10; //计算精度

//sin函数
double tsin(double x){
    double g = 0;
    double t = x;
    int n =1;

    do{
        g +=t;
        n++;
        t = -t*x*x/(2*n-1)/(2*n-2);
    }while(fabs(t) >= TINY_VALUE);

    return g;
}

int main(){
    double k,r,s;
    cout << "r = ";
    cin >> r;
    cout << "s = ";
    cin >> s;

    if (r*r <= s*s)
        k = sqrt(tsin(r)*tsin(r)+tsin(s)*tsin(s));
    else
        k = tsin(r * s)/2;

    cout << k << endl;
    return 0;
}
